Seismic Ground Motion - Dynamic Behavior of Concrete and Seismic Engineering - page 95

Chapter 3
Seismic Ground Motion
3.1. Introduction
Seisms are sudden fracture failures, with aftershock that can reach several
meters, on areas that can exceed 10,000 km². The sudden sliding emits seismic
waves that propagate in the ground, causing multi-directional vibratory movements
u i (x,y,z; t) in horizontal and vertical directions that generate vibrations on the
surface of existing structures. Depending on their amplitude, frequency and duration
characteristics, these vibrations can damage buildings or even cause their complete
collapse. Seisms not only affect man-made structures, but also lead to the damage or
collapse of “natural structures” like soils, causing liquefaction, settlement or the
formation of unstable slopes.
The main aim of “seismology engineering” is either to estimate a priori the main
features of such vibrations so that surface structures can be dimensioned safely, or to
estimate the potential damage that could accrue on pre-existing natural or man-made
structures. Whilst, on the one hand, seismology attempts to analyze the space and
time repartition of vibrations (their location, depth, size and frequency of
earthquakes), in close connection with “conventional” geologists and seismologists,
it will also attempt to quantify the associated vibrating motions, and characterize
them using parameters representing their “damaging power”. The aim is to
understand the phenomena that cause vibrations and the physical values that control
them as well as possible, so that future seismological events can be predicted.